Some of these books are informative, others are entertaining, and all of them will increase your understanding of both Mexico and Oaxaca. Some are easier to find in Oaxaca than at home, and vice versa. Many of them are out of print, but www.amazon.com [1], www.barnesandnoble.com [2], or libraries may have used copies. Take some along on your trip. If you find others that are especially noteworthy, let us know.
Links:
[1] http://www.amazon.com
[2] http://www.barnesandnoble.com